The process of dental decay is a dynamic one involving episodes of demineralization and remineralization, and may be prevented by the proper use of fluoride. The overall objectives are to increase our understanding of demineralization and remineralization processes in order to develop clinically applicable remineralization fluids and to optimize use of existing preventive agents. The mechanisms of action of fluoride which are the primary focus of this grant are the inhibition of demineralization and the enhancement of remineralization. These two mechanisms will be investigated both in vitro and in vivo using enamel surfaces. The specific aims are to test the hypothesis that acidic remineralizing fluids are more effective than neutral fluids on either surface softened or subsurface lesions; to test whether these remineralized lesions will be more resistant to subsequent acid attacks; to use in vitro pH cycling to test the ability of remineralizing fluids to prevent, arrest, and/or repair lesions; and to use an intraoral system to test the ability of remineralizing agents to enhance the ability of saliva to prevent, arrest, and/or repair lesions. The remineralization experiments will be conducted under relatively constant ion composition and will be followed kinetically. The amount, site and type of remineralization will be determined by polarized light microscopy and quantitative microradiography on the single sections. Both SEM with energy dispersive analysis nad x-ray diffraction of the lesion mineral will be used to evaluate the nature of the remineralized lesion, the size of the crystals and gross morphology. The episodic nature of dental caries will be studied using a pH cycling model in vitro and an intra-oral model in vivo. The in vivo experiments will rely on saliva as the main remineralizing agent, while test fluids will be used to "prime" the hard tissue and enhance the effectiveness of saliva. Thus, techniques for prevention and repair of enamel caries will be developed, tested and made clinically applicable.